Modeling dissolved oxygen dynamics and hypoxia

Abstract

Abstract. Hypoxia conditions are increasing throughout the world, influencing biogeochemical cycles of elements and marine life. Hypoxia results from complex interactions between physical and biogeochemical processes, which can not be understood by observations alone. Models are invaluable tools at studying system dynamics, generalizing discrete observations and predicting future states. They are also useful as management tools for evaluating site-specific responses to management scenarios. Here we review oxygen dynamics models that have significantly contributed to a better understanding of the effects of natural processes and human perturbations on the development of hypoxia, factors controlling the extent and temporal variability of coastal hypoxia, and the effects of oxygen depletion on biogeochemical cycles. Because hypoxia occurs in a variety of environments and can be persistent, periodic or episodic, models differ significantly in their complexity and temporal and spatial resolution. We discuss the progress in developing hypoxia models for benthic and pelagic systems that range from simple box models to three dimensional circulation models. Applications of these models in five major hypoxia regions are presented. In the last decades, substantial progress has been made towards the parameterization of biogeochemical processes in both hypoxic water columns and sediments. In coastal regions, semiempirical models have been used more frequently than mechanistic models to study nutrient enrichment and hypoxia relationships. Recent advances in three-dimensional coupled physical-ecological-biogeochemical models have allowed a better representation of physical-biological interactions in these systems. We discuss the remaining gaps in process deCorrespondence to: M. A. Peña (angelica.pena@dfo-mpo.gc.ca) scriptions and suggest directions for improvement. Better process representations in models will help us answer several important questions, such as those about the causes of the observed worldwide increase in hypoxic conditions, and future changes in the intensity and spread of coastal hypoxia. At the same time, quantitative model intercomparison studies suggest that the predictive ability of our models may be adversely affected by their increasing complexity, unless the models are properly constrained by observations.

Mixing in the Black Sea detected from the temporal and spatial variability of oxygen and sulfide – Argo float observations and numerical modelling

“…This process is observed around the southern coast where NEMO-0145 spent part of its lifetime, but also in the central gyre. The second demonstrates clearly that the CIL is formed not only in the coastal zone but also in the central gyre, which supports the observations of Ovchinnikov and Popov (1987) and numerical simulations of Stanev et al (2003). The CIL is refilled every year in February-March.…”

“…6a) is lower than 8 • C over the western and central Black Sea reaching 10 • C around the eastern coast. This low SST enables cold intermediate water to form over large areas (for the water mass formation in the Black Sea see Ovchinnikov and Popov, 1987;Stanev et al, 2003). The lowest SST occurs in the northwestern shelf; this low-temperature area extends southward because of the transport along the western coasts.…”

Natural and human-induced hypoxia and consequences for coastal areas: synthesis and future development

“…The numerous physical and biogeochemical processes regulating DO concentrations make it challenging to understand coastal hypoxia based on observations alone. Biogeochemical models that include the oxygen cycle have contributed to improved understanding of diverse aspects of hypoxia such as for example, processes responsible for the development of hypoxia, controls on extent and temporal variability, its impacts on biogeochemical cycles, and predictions of climate change responses (Peña et al, 2010). Moreover, recent advances in 3-dimensional coupled physical-chemicalbiological models have contributed to the improved quantitative understanding of the physical and biological processes leading to hypoxia (e.g.…”

Determination of Water Quality Degradation Due to Industrial and Household Wastewater in the Galing River in Kuantan, Malaysia Using Ion Chromatograph and Water Quality Data

“…Under oxygenated conditions, aerobic oxidation of organic nitrogen and phosphorus compounds due to microorganisms (Equation (1)) and nitrification caused by nitrifying bacteria (Equation (2)) are facilitated [22][23][24]. Thus, organic nitrogen and phosphorus compounds were decomposed to NH 3 , which dissolved to form NH 4 + in the water phase.…”

“…Secondly, NO 3 − -N in TIN was reduced to N 2 gas through denitrification by denitrifying bacteria. In contrast, organic and inorganic phosphorus were not reduced to gas by biological reactions [22][23][24][25][26][27].…”